Draft control



March 21, 1939. H. JQRosE ,1 1,

- DRAFT CONTROL Filed Ma a, 1936 Harold J 98! ATTORNEY Patented-Mar. 21,1939 2451,1142 DRAFT CONTROL Harold J. Rose, Pittsburgh, Pa., assignorto The Philadelphia and Reading Coal and Iron Company, Philadelphia,Pa.,

Pennsylvania a corporation of Application May s, 1936, Serial No. 78,549.10 Claims. (01. 122-4) This invention relates to a method and apparatusfor controlling drafts for solid-fuelburning furnaces withinpredetermined limits. The majority of such heating apparatus orfurnaces, especially those used for domestic purposes, depend uponnatural draft for proper combustion of the fuel. a

This natural draft when furnished by. a chimney or stack is highlyvariable and depends upon a great number of factors such as thecomposition, temperature, and volume of the products of combustion, thetemperature and humidity of the outdoor air, and the velocity anddirection of wind. By reason 01' the variability of conditions,uncontrolled natural draft is not satisfactory for year round operation,especially when used for automatically regulated heaters.

One object of my invention is to maintain natural draft available forimmediate use by the heat gr at any time within certain predeterminedlimi Further objects of my invention are to supplement natural draftwhen necessary, utilizing excess heat from the heating apparatus, torelease or diminish excess draft, and to prevent down drafts or negativedrafts from reaching the fuel in the heater.

Since combustion gases are somewhat heavier than air at the sametemperature due to their high content of carbon dioxide, it is necessaryto maintain these combustion gasesat a. relatively high temperature inthe chimney in order to create a natural draft. This is rather diflicultto do in certain seasons, especially if the chimney becomes, damp byreason of rains or moisture condensation.

In accordance with my invention I therefore provide means for passingheated air into the chimney which has the dual effect of reducing thedensity of the combustion gases, and increasing their drying P wer. Thistends to maintain the chimney warm and dry at all times and the desireddraft is thus always available for immediate use.

' Wind direction and velocity are also important factors and may verymaterially affect the amount of draft available even though the chimneyis maintained warn'iv and dry. If the wind produces a lower pressure atthe top of the chimney than at the bottom thereof, excessive draft willbe created and therefore a further object of this invention is toautomatically by-pass cold air into the'chimney when such excessivedraft is created. Wind may also create a pressure at the top of thechimney and cause down drafts and it is, therefore, also preferred toprovide an automatic release for such down drafts before they reach theheating apparatus. a

The smaller the heating apparatus, the greater difficulty is normallyencountered with draft conditions and my invention therefore findsparticular application to small domestic heating devices such as thoseused for burning solid fuel to heat water. My invention is alsoparticularly applicable to and has special advantages when employed incombination with heating, apparatus such asshown and described in theco-pending application of R. Johnson, Serial No. 64,835, filed February20, 1935.

The foregoing and further objects and advantages of this invention maybe better understood from a consideration of an embodiment thereofillustrated in the drawings, in which the figure illustrates a verticalcross section of a domestic water heater of the solid-fuel-burningradiation type.

In the drawings, numeral I indicates a shell which may be of acylindricalor other shape and defines a fire-pot of a solid-fuel-burningfurnace. Solid fuel may be supported upon the grate 2, which may be ofany suitable construction for allowing a combustion medium, such as air,to

pass upwardly therethrpugh. This grate may be supported in any desirablemanner, as by an arm 2a. Fuel is preferably fed to the fire-pot,

as defined by the grate 2 and the shell I, through a magazine indicatedgenerallyat 3. This magazine comprises a storage compartment 3a abovethe shell I and is preferably provided with inwardly sloping side walls4 and vertical depending walls 5 for directing the fuel into thefire-pot. The magazine should be tightly closed as by the lid 6, havinga handle I.

Spaced from the shell I, and surrounding the same, is a jacket made upof an outer wall 8 and an inner wall 9 designed to contain the water I0to be heated. An inverted frusto conical section II, and an annularmember I2 are positioned to cooperate with the shell I in defining aclosed air space I3-between the shell I and the wall 9. The outerfluid-containing jacket and the magazine are preferably provided with aheat insulating layer I4 which may be of some relatively non-conductingmaterial or provided with a reflective outer surface as is understood inthe art. Water to be heated is supplied to the outer Jacket by pipe I5and the heated water is drawn off through the pipe I6.

Air for combustion may be supplied to the ash pit I1 and grate 2 bymeans of the opening I8.

The ash pit I1 is prefcgably provided with a section 20 of suitable apeto cooperate with a tightly fitting door 2| provided with a lockinghandle 2la. Suitable means may also be provided'for shaking the grates2.

The top of the shell I is preferably spaced from the lower end of thedependingwall 5 a sufiicient distance to allow the products ofcombustion from the fuel to pass out through the opening 22 to a pipe 23which leads to the flue or stack. The lower end of pipe 23 communicateswith the air space l3 by means of an extension 24 and may be suitablyreinforced and held in place by the tie-rod 25. Air supplied to thespace l3 by way of an opening 26 is preferably deflected to circulatethrough the air space by the baflie 21. The passage of combustion airthrough the fuel and the passage of air through the space l3 are bothregulated by a single valve member 28 which may be pivoted about a rod23 and positioned near the juncture of the pipes 22 and 23.

In one position the damper 28 rests upon the supporting stud 30 andsubstantially closes the passage leading from the air space l3 to theflue. A small opening 3| may be provided in the damper to allowcontinuous fiow of a minimum amount of air or products of combustion atall times. When the damper 28 is swung to the other extreme position,the opening 22 is substantially closed and the fire is effectivelychecked. Suitable handle or other means may be provided on the shaft 29for the operation of this valve member.

To provide for the release of gases from the pipe 23 when a'condition ofdown draft is ere.-

' ated I provide the damper 32, which may be mounted on the rod 33 forpivotal movement. Suitable weighting means 34 is preferably provided tosusbtantially balance thisdamper on the rod 33. Under conditions ofpositive draft, the lower end of the damper is held against the stop 35and is thus maintained closed. When the draft is reduced to zero or acondition of down draft is created, this damper will automatically openand allow air rushing down the chimney and into the pipe 23 to escapeinto the room.

- In order to take care of and reduce excess drafts, the damper 35 ispivotally mounted on the rod 31 and suitably weighted by means of theweight 33 so that under all normal conditions it remains in a verticalclosed position. When excessive drafts are created, however, the lowerportion of this damper will swing inwardly, allowing cold air from theroom or cellar to pass up into the stack and reduce its temperature.This damper also serves to relieve the fireimmediately of excessivedraft and since it swings into the flue, it functions to throttle the'fiow of gases from both the openings 22 and 24.

The operation of the heating apparatus is generally similar to thatdescribed in the application of Raymond Johnson Serial No. 64,835, filedFebruary 20, 1936, and heat is transferred from the solid fuelin thefire-pot I to the water l0 principally by radiation.

My invention is designedto particularly take advantage of the air spacebetween the water jacket and the shell I and to utilize air heated bypassage through this space to maintain the flue and chimney in a warmand dry condition. While in the embodiment of my invention illustratedthe air is heated by both the fire-pot and the water jacket, it isevident that the excess heat may be extracted from either the fire-potor the fluid being heated alone.

Draft regulation in accordance with my invention has especial advantageswhen used in combination with a radiating solid-fuel heater. Forexample, the withdrawal of heat from the space l3 and discharge ofheated air to the stack when the fire is checked assists the thermalvalve action of the radiation heater by immediately cooling the outer orradiating surface of the shell I. Thus, when the fire is on draft andthe damper 23 rests on the stud 30, only a minimum amount of heat iswithdrawn from the air space l3, the bulk of it being transferred to thewater I0. As soon as the fire is checked by moving the valve 28 to theother'extreme position, the fiow of cold air in through the passageway26 and the withdrawal of heated air through the passageway 24facilitates the thermal valve action of the radiation heater by quicklycooling the radiating surface and preventing the water II! from becomingoverheated. Overheating or what is known as overruns are effectivelyeliminated where my improved draft regulation is applied to a radiationheater.

The net result of this improvement when the fire is banked is that thefire is not caused to burn faster than necessary to supply hotcombustion gases to the chimney with the attendant overheating of thehot water. After a heater has been operating at high capacity for sometime and the fire is checked the surplus heat is usefully applied tomaintaining the chimney draft and preventing it from overheating thewater. The use of heated air to maintain chimney drafts in general ascompared with heated combustion products is especially advantageousbecause tests have shown that the combustion gases from anthracite coalmust be heated as much as 40 F. hotter than air to give the same drafteffect.

The two valves 32 and 36 have a special utility in combination with aheater embodying my invention, since the combination provides aneffective control and maintenance of available draft at all times withinpredetermined limits and under all possible conditions. When the fire-ison draft it is desirable that some air be drawn through the space l3 andpassed to the chimney since this has the action of supplementing theheat of the products of combustion and of decreasing their density andalso reducing the tendency for moisture to condense in the chimney.

For the reasons discussed above, I have found that it is distinctlyadvantageous to correlate the flow of primary air for combustion withthe flow of heated air to the stack. Any suitable means may be employedfor this purpose eitherat the outlet from the furnace as shown, or atthe inlet as in openings I 8 and 26.

However, it is to be distinctly understood that my invention is notlimited to such features but individually controlled dampers may beemployed at any available positions in' the system. For example,individual manually operated dampers may be employed in the openings and26, min the openings 22 and 24, or in the openings 22 and 26, or even atall four positions.

The terms and expressions which I have employed are used as terms ofdescription and not of limitation, and I have no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize thatvarious modifications are possible withinthe scope of the inventionclaimed.

the draft therein exceeds a No claim is made herein to the particularconstruction of the damper 28 illustrated in the drawing, since thisfeatureis claimed in the copending application of Hilmar R. Hagen SerialNo. 193,838, flled March 4, 1938.

I claim:

1. Heating apparatus comprising a fire-pot for burning solid fuel, meansfor confining a liquid imedium to be heated in a position spaced from awallet said fire-pot and arranged to transfer heat from said fire-potwall to said confining means principally by radiation, means foradmitting air to the space between the fire-pot and said means, andmeans for conducting heated air from said space to a stack 2. Heatingapparatus comprising a. solid-fuelburning fire-pot, means confining afluid medium spaced therefrom and arranged to be heated principally byradiation, means for admitting primary air to said fire-pot forcombustion of fuel therein, means for admitting air to the space betweensaid flre-pot and confining means, a conduit for conducting products ofcombustion to a stack, means providing the only outlet from said spacefor admitting regulated quantities of heated air from said space to saidconduit, means for introducing cold air into said conduit whenpredetermined amount, and means for allowing a gas to escape from saidconduit when a positive pressure is created therein.

3. In a solid fuel burning water heater, a flrepot for burning solidfuel, a water jacket laterally spaced from and arranged to receive heatfrom a wall of the flre-pot principally'by radiation, means forintroducing primary air into said fire-pot to support combustiontherein, means for passing controlled quantities of products ofcombustion from saidflre-pot to a stack, means 1 for introducingsecondary air into the space between the flre-pot and jacket in heatexchanging relationship with said water jacket, and means for passingregulated quantities of said heated secondary air to said stack when theflre in said fire-pot is. checked 4. A method of maintaining a stackwarm and dry to provide efficient natural stack draft for asolid-fuel-buming heater comprising, flowing primary air through a bedof fuel for combustion thereof in said heater, flowing additional airinto heat exchanging relation with said fuel but out of contacttherewith, passing the products of said combustion and the additionalheated air to said stack, and regulating the flow of said products ofcombustion and heated air to the stack to amounts inversely proportionedto each other so that saidheated air supplements the effect on the stackdraft of said products of combustion when the flow of the latter isreduced or checked. l

5. A method of maintaining a stack warm and dry to provide an efllcientnatural stack draft for a solid-fuel-burn'ing water heater comprisins.flowing primary air through a bed of fuel for combustion thereof in saidheater, flowing additional air ,into heat exchanging relation with saidfuel and said water but out of contact therewith, passing the productsof said combustion and the additional heated air to said stack, andregulating the flow of said products of combustion andheated air to thestack to amountsinversely proportioned to each other so that said heatedair supplements the effect on the stack draft of said products of combusucts to the stack.

tion when the flow of the latter is reduced or checked.

6. The method of maintaining efficient natural stack draft available fora solid-fuel-burning heater in which a confined fluid medium is heatedprincipally by radiation of heat from a fire-pot wall across an airspace comprising, flowing primary air through said fire-pot forcombustion of fuel therein, flowing additional air into heat exchangingrelation with said fuel but out of contact therewith, passing theproducts of said combustion and the additional heated air to said stack,and regulating the flow of said additional heated air so thatsubstantial quantities thereof are passed to the stack to supplement theeffect of the products of combustion on the stack draft only when theflow of the latter is reduced or checked.

'7. The method of maintaining efficient natural stack draft avilablefora solid-fuel-burning heater in which a confined fluid medium is heatedprincipally by radiation of heat from a flrepot wall across an air spacecomprising, flowing primary air through said fire-pot for combustion offuel therein, flowing additional air through said space in heatexchanging relation with said medium and the fire-pot but out of contactwith the fuel, passing the products of said combustion and additionalheated air to the stack, and regulating the flow of said heated air toincrease the amount thereof when the flow of products of combustion isreduced or checked.

8. The method of maintaining efllcient natural stack draft available fora solid-fuel-buming hot water heater in which the water is heated in ajacket principally by heat radiated laterally thereto across an airspace from a fire-pot wall comprising, flowing air through the flre-,pot for combustion of fuel therein, flowing a stream of additional airthrough said space, passing the products of said combustion to thestack, and passing said heated air to the stack when the flow ofproducts of combustion is reduced or checked to remove excess heat fromthe heater and to supplement the effect on the stack draft of theproducts of combustion.

9. Apparatus for heating comprising a jacket for containing a fluidmedium to be heated arranged to deflne a substantially vertical centralopening, a fire-pot for burning solid fuel disposed wholly within saidopening, said fire-pot having a wall spaced from said jacket, saidjacket being constructed and arranged so that heat received by saidJacket from said fire-pot is transferred thereto from said wallprincipally by radiation, and means for passing a stream of air throughthe space between said wall and "Jacket and thence to a stack when theflre in said fire-pot is checked.

10. Apparatus for heating comprising a jacket or containing a fluidmedium to be heated,

means for introducing and removing fluid from said jacket, meansincluding walls spaced laterally from said jacket for defining a solidlump fuel burning fire-pot. said jacket substantially enclosing the heatradiating surface of said walls and being constructed and arranged sothat heat received by said jacket from said flre-pot is transmittedthereto principally by radiation from said walls, means forflowingastream of' air to be heated through the space between said wallsand jacket, and means for passing said heated air to a stack in. amountsproportioned inversely to the amounts of combustion prod-

